Process of preparing chromates of lead.



m'rnn sTaTns PATENT oTTTaoE. ALEXANDER S. RAMAGE, 0F BUFFALO, NEW YORK, ASSIGNOiRl T6 INTEItNATlbll'AIi. COLOR & CHEMICAL ('JQMPANY, INCORPORATED, OF DETROIT, MICHIGAN, A COR- PORATION OF NEW YORK.

- rnocnss or PREPARING cnnoivrarns or LEAD.

No Drawing. L

To all whom it may concern:

Be it known that I, ALEXANDER S. Rant AGE, a subject 'of the King 'of Great Britain, residing at Buffalo, in the county of Erie and State of New York, have inchrome-yellow pigments. As is well known,

these pigments possess excellent covering, lasting and inhibitive properties, but as heretofore prepared, they have been too expensive to permit their universal use.

In the preparation of chrome yellows 'according to the present invention, I may start either from piglead or lead dross, or directly from the sulfid ores of lead. Irrespective of the startingmaterial, the first step consists in forming a. pure sulfate of lead, which is'thereafter converted into the chromate. Or instead of preparing sulfate of lead by the methods hereinafter described, I may start directly with sulfate of lead prepared by other methods orderived from other sources.

lVhen pig lead or equivalent form of the metal is used as thestarting material, itis melted,-granulated or'feathered in water, and dissolved in diluted nitric or acetic acid. The resulting lead nitrate or acetate is run into wooden tanks and precipitated by thev molecular equivalent of sulfuric acid. The nitric or acetic acid is thusset free without material dilution, and may be.directly utitizead for dissolving further quantities of 'The lead sulfate pulp from which the acidhas been decanted is run into a .wobden filter tank provided with a false bottom covered with asbestos cloth, and fitted, below' the false bottom, with vacuum and waterinlet connections. The sulfate 'is drained as thoroughly as possible, preferably with the aid of the vacuum, and water is'then introduced very slowly from below, whereby the remaining acid is displaced upwardly and collected at the overflow. By proceeding in this way, the losses ofacid are mininiized, and it has been found practicable to; reduce them to approximately one per Specification of Letters Patent.

cent. of the total quantity of acid used at each operation.

Patented Jan. 18,1916. Application filed April 16, 1915. Serial N01 21,872."

of sodium bicromate, and the whole is.

thoroughly boiled; thereafter, a suitable quantity of caustic soda is added, and the boiling,is continued until the conversion of the lead-into the chromate is complete. The whole operation may be' finished in about one hour, and the resulting chromate of lead,

after careful washing and draining, is

pulped with about twenty per cent. of its weight of oil, this pulping process being carried out in the same manner as is commonly practised in the case of. white lead pigments. Inasmuch asthe several lead precipitates have at no time been permittedv to -become dry, the resulting suspension in oil is exceedinglyperfect and almost colloidal in character.

Suitable proportions of reagents for the conversion of lead sulfate to chromate are about 246 parts by weight of sodium bichromate, and about 200 parts by weight of causticsoda, to each 1000parts of lead sulfate; but these proportions may be varied according tothe shade of yellow desired in the product. I v

- It will be observed that according to the above description the lead sulfate is boiled in presence of. the sodium bichromate bep 'fore the caustic soda is added. If this procedure is not followed, or if the sodium bichromate and caustic soda are-introduced simultaneously, an objectioriably flocculent precipitate will'be produced. For example,

andsoda" in the-order named yields a pulp the successive introduction of the bichromate Y or paste weighing about sixteen pounds per gallon, whereas if these components are added simultaneously, a paste weighing but twelve pounds per gallon. will result.

Lead dross may betreated in the same manner as metallic lead.

As above stated, the source or mode of production of thelead sulfate is not material to that portion of my invention which per-" tains to the conversion of the lead sulfate to the chromate; and the sulfate may thereglowing any of the recognized methods. I

The expression. a chromate of lead is employed herein to include the basic chromates of lead.

I claim:- I 1. A cyclical process of making a chromate of lead, which consists in dissolving a lead-bearing material in an acid, precipitating the lead as sulfate and setting freethe solvent acid by addition of sulfuric acid, Washingthe precipitated sulfate and digesting the same in presence of an alkali metal chromate, then adding an alkaline reagent, and applying the liberated solvent acid to fresh portions of the lead-bearing material.

2. A cyclical process of making a chr0- mate of lead, which consists in dissolving a lead-bearing material in an acid,cpr ecipitating the lead as sulfate and setting freethe solvent acid by addition of sulfuric acid,

washing the precipitated sulfate and 'di est ing the same in presence of sodium'bic romate, then addlng caustic soda, and applying the liberatedsolvent acid to fresh por- 'tions of the lead-bearing material.

3. In: a process of producing a chromate of lead, the step which consists in digesting lead sulfate in presence of a bichromate, and then adding an alkali, thereby convert ing the sulfate of lead into a'chromate.

then adding a caustic alkali, and continuing 4. In a process of producing a chromate' of lead, the step which consists in digesting lead sulfate in'presence of a bichromate,

the digestion to convert the sulfate of lead 40 i into a chromate.

In testimony whereof I aflix my signature.

ALEXANDER S. RAMAGE. 

